It has to do with the power efficiency, conduction angle, and linearity.

Class A amplifiers are very linear amplifiers and are theoretically (maximally) 25% efficient. Even when they are not in use, current is flowing, that is the standby power is not 0. The conduction angle is 360 degrees

Class B amplifiers are less linear and are theoretically (maximally) 79% efficient. Class B amplifiers conduct half the time, conduction angle = 180 degrees. However since they turn off and on, it makes the transfer characteristic very non-linear and results in distortion.

Class C amplifiers are theoretically 100% efficient. They use a tuned "tank" circuit to control when the amplifier is conducting. These are very nonlinear amplifiers.

Class D amplifiers... I actually never learned these very well because... well... the professor said we didn't need to know them... They use a PWM technique to generate pulses which control switches. If you figure out how this works, tell me!!!!!!!

CLASS D AUDIO AMPLIFIERS ARE SIMILAR IN OPPERATION TO SWITCHED MODE POWER SUPPLIES RETURNING TYPICAL EFFICIENCIES OF 95%.I HAVE USED THE POWERLITE SERIES OF AMPLIFIERS TO RUN BASS END AT SOME GIGS,HOWEVER,AT THE RISK OF SOUNDING OLD FASHIONED,I DO LIKE A POWER AMP FULL OF TO-3 O/P DEVICES,A VERY LARGE TOROID AND TWO MASSIVE CAPS.THEY SOUND SO MUCH BETTER AT LOW FREQUANCIES.

i believe the 95% efficiency was referred to the switch mode power supply.

dont forget about the class AB, G, H, another good amp design is operating the output stage at class AB and the rest of the circuit at class A

besides, music is a very subjective thing, what may sound good to another may not suit another one. so even if you have a horrible amp but you like the sound coming from it, any other amp is no better than your horrible amp.

Class D amp - the output waveform is the same as the input waveform over 360 degrees of the operating cycle, except for the residual distortion. also the D amp technically differs from the A amp this way, the input waveform is converted into a pulse-modulated form prior to amplification and is then reconstituted into its original waveform following amplification. this kind of amp is usually designed with a linear transfer mode but it can be also operated with expansion or compression transfer characteristics.

Class G amp - the output is the same as the input which the A amp also does. however, the G amp has a 2 level operation, any signal up to the middle range is amplified by the first level and signal above the middle range is amplified by the second level. the output from the 2 section is combined to reconstitute the original waveform. (note: if you are familiar with active crossovers they are somewhat the same except the output of the active is injected to their respective amps. the output of the active is not recombined) B)

Class H amp - the output is also the same as the input but this amp operates at a variable -level power supply. when the amp is operated at low level signal the amp is powered at alow voltage supply. and when it is processing a high level signal the supply voltage is automatically increased as needed for it to exceed the amplituted of the signal that is being processed.

i will not discuss how this amps sounds becoz i always maintain that music is highly a subjective matter. a good sound to you may not be good to another.